(1) Field of the Invention
This invention relates to a novel zeolite powder having high flowability, a process for preparing the zeolite powder and a detergent composition containing the zeolite powder.
(2) Description of the Prior Art
Zeolites are excellent in various properties such as the ion exchange property and absorbing capacity, and they are utilized as catalysts, ion exchangers, adsorbents, etc. in the chemical industry and other various industries.
Zeolites are used in the form of powders, pellets and granules. Powdery zeolites have an especially strong cohesive force among particles and the flowability of powdery zeolites is especially poor, and among various powders, zeolite powders are especially difficult to handle. Accordingly, problems are readily caused by clogging at the transportation (particularly, pneumatic transportation), feeding and storing steps which occupy important portions of the process handling zeolite powders, and therefore, efforts are made to prevent occurrence of clogging.
This clogging phenomenon takes place because of formation of so-called bridges and hindrance of free flowing by these bridges. These bridges are formed owing to an excessively high cohesive force of zeolite powders and a poor flowability. Clogging takes place not only at a discharge opening of a store tank hopper but also through a course of transportation of zeolite powders by a feeder or transporting machine, particularly, by a pneumatic coveyor, and problems are often caused by clogging. Once clogging occurs, the operation adaptability is drastically degraded in the utilization of zeolites.
Various measures for preventing the occurrence of clogging due to bridging have been made in processes handling powders. For example, the shape, dimensions and material of the store tank, the size of the outlet and the inclination angle of the vessel have been taken into consideration, and, for the withdrawal of powders, there are adopted special methods such as a shaking method using BINACTIVATOR (supplied by Vibra Co.) or the like and an air-utilizing method employing a pneumatic knocker or an aeration unit for blowing compressed air.
In the case of zeolites, however, since single particles have such a small size as 1 to 5 microns, and they have a moisture-absorbing property and a very strong cohesive force as pointed out hereinbefore, it is admitted that strong measures for preventing occurrence of bridging are necessary. Accordingly, a zeolite product is handled in the form of an aqueous slurry, or it is once granulated to facilitate handling at the transporting and storing steps and is pulverized again before it is actually used. Thus, special care has to be taken in handling zeolites.
Water-insoluble aluminosilicates (i.e., zeolites) have been proposed to be used as a builder for detergent as taught in Japanese Laid-open patent applications No. 12,381/75, No. 21,009/75, No. 53,404/75 and No. 70,409/75. These known aluminosilicates are represented by the following general formula (2): EQU x'(M'.sub.2 O or M"O).(Al.sub.2 O.sub.3).y'(SiO.sub.2).w'(H.sub.2 O) (2)
wherein M' stands for an alkali metal, M" stands for an alkaline earth metal exchangeable with calcium, and x', y' and w' signify mole numbers of the respective components and ordinarily, x' is in the range of 0.7.ltoreq.x'.ltoreq.1.5, y' is in the range of 0.8.ltoreq.y'.ltoreq.6, and w' is an optional positive number.
Of water-insoluble aluminosilicates represented by the above general formula (2), a completely crystalline 4A type aluminosiicate (Na.sub.2 O.Al.sub.2 O.sub.3.2.0SiO.sub.2.4.5H.sub.2 O) is most important and is now popularly used as a detergent builder.
Crystalline aluminosilicates represented by the 4A type aluminosilicate are used in the form of a fine powder having an average particle size of 1 to 10 microns, a spray-dried secondary particle having an average particle size of 100 to 300 microns or an aqueous slurry having a solid content of 40 to 60%. However, these crystalline aluminosilicates have the following defects. Namely, the crystalline aluminosilicate reacts with a silicate such as sodium silicate contained in a detergent composition to increase the method of insoluble matters (this tendency is especially conspicuous when both the aluminosilicate and sodium silicate are co-present in a detergent slurry). Furthermore, if the water content is reduced excessively when the detergent slurry is powdered by spraying, association of the crystalline aluminosilicate takes place and the amount of the insoluble matter is further increased. This insoluble matter, unlike the finely divided crystalline aluminosilicate, is deposited and accumulated on clothes while the clothes are washed repeatedly by using such detergent, and the touch and feel of the clothes is gradually degraded. Since crystalline aluminosilicates are excellent as detergent builders, elimination of these defects has eagerly been desired.